With so few good new titles being released these days, especially by major studios, I figured I'd make a thread for everyone to share your favourite classic or older games, especially if they're lesser-known titles that others might have missed at the time.
I'll open with The Saboteur (2009), Mercenaries (2005) and Saints Row 2 ( The 2008 original)
All great options. Another really good older RTS is Star Wars: Empire at War. Still one of the best Star Wars games ever released.
Edit: I also loved the original Stronghold games, especially Crusader.